This invention relates to spot-type disc brakes and more particularly to a brake shoe holding device therefore.
Brake shoe holding devices for spot-type disc brake including two support members spaced apart from each other with a brake shoe slidably guided on the support members in the direction of brake application and positively connected with the support members in the peripheral direction of the brake disc such that at least in the presence of increased brake-applying forces the frictional force occurring at the brake shoe is transmitted to both support members because they ensure even wear of the brake shoes and because the distribution of the frictional force on both support members results in good utilization of the material.
In a known spot-type disc brake disclosed in German Patent No. DT-AS 1,575,920, the brake shoe holding device includes two supporting bolts forming a disengageable screw connection with the brake housing and extending through two openings in the pad backing plate with clearance, the center-to-center distance between the two openings being smaller than the center-to-center distance between the two supporting bolts by the amount of the maximum elastic deformation of a supporting bolt.
The disadvantage of this known brake shoe holding device is that it allows brake-shoe replacement only if the supporting bolts which receive the frictional force, are unscrewed. As a result, the replacement of brake shoes requires the removal of several screws which must be tightly seated to provide the functional safety of the brake. Pad replacement is thus complicated and entails a safety risk which should be avoided by all means. Moreover, the dimensional tolerance for the center-to-center distance between the supporting bolts which is due to the screw connection would be assumed to reach a magnitude at which distribution of the frictional force on both supporting bolts in a desired ratio is not reliably attainable.
Another brake shoe holding device of the above type described in British Patent No. 938,977 includes two spaced plane plate-type calipers straddling the outer periphery of a brake disc and having recesses on both sides of the brake disc to receive the brake shoes comprised of a backing plate and a friction pad. The backing plates of the brake shoes have at their radially inward and radially outward edge slots for positive engagement with the calipers. In this known arrangement, the frictional forces occurring at the brake shoes when the brake is actuated are transmitted to both calipers because the calipers, in the direction of application of the frictional forces, have a low inherent rigidity and obtain the rigidity required for taking up the forces only by the arrangement of the pad backing plates in the form of a transverse wall. It is a substantial disadvantage in this known brake shoe holding device that the brake shoes may become jammed relative to the calipers so that actuation of the brake is impaired. Further, brake shoe replacement is only possible after unscrewing and lifting off of the brake caliper from the brake disc.